While we’ve suspected that Office was coming for a while now, Microsoft hasn’t been all that forthcoming with its intentions for the software, which was initially rumored to hit the iPad this year.

Microsoft has a shrewd plan for Office Mobile: While users can view documents for free, editing them requires a subscription to Office 365, which runs at least $4 per month. Unsurprisingly, Windows Phone Office users can edit for free.

The big question is this: Why is Microsoft bringing Office to Android and iOS at all? Shouldn’t Office be the kind of thing that gets consumers to buy a Windows device over those of competitors?

The answer is actually really simple: Microsoft isn’t stupid. It knows there’s a lot more money in creating Office for iOS and Android than limiting it to Windows. Recent forays into hardware aside, Microsoft is still mostly a software company. And it wants people using its software.